This invention relates to a parcel containing an inhibitor (hereinafter referred to as "inhibitor parcel"), and more particularly to an inhibitor parcel used for transporting or preserving metallic, electronic and semiconductor products, devices, parts and the like, as well as to a method for preserving metallic, electronic and semiconductor products, devices, parts and the like by the use of said inhibitor parcel and parcelled articles used for their preservation.
Further, this invention relates also to a combined use of a sheet-form drier in the abovementioned method for preservation and the abovementioned parcel. Furthermore, this invention relates also to the above-mentioned inhibitor which does not evolve heat rapidly and is safe and easy to handle even if allowed to stand in the presence of air before or after its use. In this specification, the inhibitor parcel may, at times, be simply referred to as "inhibitor".
In the preservation of copper, silver, aluminum and the like used in electronic devices or electronic parts, the rusting or corrosion caused by water, oxygen, acidic gases, metal halides and the like is the most important problem.
A semiconductor is produced by plating silver or gold onto a thin plate of copper alloy or iron-nickel alloy to form a lead frame, bonding IC chips thereto by the use of an adhesive, connecting the IC chips to the lead frame with gold wires, and thereafter sealing the whole with a resin.
When the lead frame is exposed to air, however, its alloy surface becomes rusty. As such, the use of silver- or gold-plating is impracticable and solderability to a printed base deteriorates. Further, aluminum is used in IC chips as a wiring elementary material, and the aluminum is rusted by the acidic gases and metallic halides vaporized from the adhesive or sealing material and the water and oxygen present in the atmospheric air, which causes breakage of wirings, etc.
As methods for preventing these rusting phenomena, the following methods have been known hitherto.
(1) Shortening of preservation period:
In the production of semiconductors, various steps of production are usually carried out at different places. If the periods of time necessary for transportation between different places and storage in warehouses are shortened as much as possible, rusting may be prevented. However, this method is disadvantageous in that the production cannot be designed intentionally and excessive equipments and staffs must be always arranged. Further, when semiconductor parts are produced in oversea lands, the transportation of parts takes a long period of time, due to which the shortening of period necessary for storage is limited.
(2) Selection of adhesive and sealing material:
In order to reduce the quantities of organic acids, halogen compound and the like vaporized from the epoxy resin, silicone resin and the like used as an adhesive or a sealing material, selection of the materials and adoption of more desirable processing conditions have been studied. However, this method requires a very delicate quality control, and it is quite difficult to supply stable products by this method.
(3) Replacement of gas:
In Japanese Patent Application Kokai (Laid-Open) Hei 1-139370, a method which comprises replacing the air in a vessel with nitrogen gas is proposed. However, this method also has the following problems: (i) it requires a particular apparatus for the replacement of air with nitrogen gas, (ii) the gas in the vessel is difficult to replace with nitrogen gas effectively, and the object cannot be achieved even by using a large quantity of nitrogen gas.
(4) Combination of replacement with nitrogen gas and a drier:
In Japanese Patent Application Kokai (Laid-Open) Hei 1-139370, a combination of replacement with nitrogen gas and the use of drier is proposed. However, this method also has problems similar to those in Method (3).
On the other hand, in Japanese Patent Publication Sho 62-40880, the use of an oxygen absorbent was disclosed as a method for preventing the rusting of metals. According to this method, a metal and metallic product is packed into a gas-barrier type parcelling material together with a permeable diffusing-parcel containing an oxygen absorbent and the whole is tightly sealed, whereby the sealed system is brought into an oxygen-free state and rusting of the metal is prevented.
As the oxygen absorbent, many substances have hitherto been proposed. They include, for example, those containing as main component sulfites, bisulfites, ferrous salts, dithionites, hydroquinone, catechol, resorcin, pyrogallol, gallic acid, Rongalit, ascorbic acid and/or its salt, isoascorbic acid and/or its salt, sorbose, glucose, lignin, dibutylhydroxytoluene, butylhydroxyanisole, powdery metals, and the like.
However, all the above-mentioned oxygen absorbents have a general disadvantage that their oxygen absorbing reaction does not progress in the absence of water. That is, these oxygen absorbents composed mainly of the above-mentioned compound or powdery metal can absorb oxygen only when they are mixed with water or a water-holding substance or they can utilize water vaporized from the material to be preserved.
Accordingly, for rust prevention of metals readily corrodible by water, the above-mentioned oxygen absorbents are not satisfactory because the moisture generated from the oxygen absorbent rusts the metal surface and makes it impossible to achieve the object, namely preservation of metal without deterioration in its quality.
As an improvement of such prior rust prevention techniques using an oxygen absorbent, there have been proposed the method of Japanese Patent Application Kokai (Laid-Open) Sho 63-198962 which comprises using an oxygen absorbent comprising an unsaturated fatty acid or a fatty oil composed of an unsaturated fatty acid, a transition metal or a transition metal compound and a basic substance, and the method of Japanese Patent Application Kokai (Laid-Open) Sho 64-67252 which comprises using an oxygen absorbent comprising an unsaturated fatty acid compound, a basic substance and an adsorbent.
Now, in the mechanism of quality deterioration, particularly rusting, of semiconductor devices or semiconductor parts, the rust caused by water appears most rapidly. Accordingly, the water in the preserved system must be removed as rapidly as possible. For this purpose, a method of using an oxygen absorbent and a drier in combination is disclosed in Japanese Patent Application Kokai (Laid-Open) Sho 56-153788. According to this method, however, the water in oxygen absorbent is gradually lost as it shifts to the drier and, as the result, oxygen absorbing performance is also lost. Thus, it has sometimes happened that the oxygen permeates into the parcel through the packaging film, even though it is very slight in quantity, elevates the oxygen concentration in the system, until the inhibitory effect can be deteriorated gradually.
When the above-mentioned oxygen absorbent compositions containing an unsaturated fatty acid compound as a main ingredient (Japanese Patent Application Kokai (Laid-Open) Sho 63-198962 and Sho 64-67252) are parcelled into a conventional permeable diffusing-parcelling material, the water present in the system for preserving electronic devices and parts, particularly semiconductor devices or semiconductor parts, is lower in absorption speed than the oxygen in the system because of the nature of the permeable diffusing-parcelling material, and hence no satisfactory inhibitory effect can be achieved by such a technique.
Further, there is an important problem regarding the handling of preservative, though it may not be directly related to prevention of semiconductor devices and semiconductor parts from deterioration. Thus, it is a problem that, if a preservative before or after use is allowed to stand in the atmospheric air, it generates heat and can fire when a large quantity of preservative is left in lump.
Further, as yet another problem, the following should be pointed out. Thus, as a permeable diffusing-parcelling material, a laminated product prepared by sticking paper and perforated plastic film is conventionally used. Since usual paper is used in this type of parcelling material, however, paper powder is generated when the ribbon-wise linked plural inhibitor parcels made of such a parcelling material are cut into individual parcels, and the powder adheres to the surface of parcel. Further, fine powder of the inhibitor composition leaks out of the parcel through the pores of plastic film and paper layer. The paper powder and fine powder of inhibitor composition thus formed pollute the semiconductor parts and the like or the material to be preserved and causes short-circuiting or rusting of the electric circuit, and thereby bring about undesirable results.